Vehicle speed control system

ABSTRACT

This invention relates to a vehicle speed control system, configured with off-road performance features, that will allow the driver to travel at a set speed in a smooth, controlled manner on various unmaintained surfaces without requiring the driver to press the brake or accelerator pedal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional patent application of U.S. patentapplication Ser. No. 14/650,456, filed Jun. 8, 2015 and published asU.S. 2015/0321671 A1 on Nov. 12, 2015. U.S. 2015/0321671 A1 is theNational Phase of International Application No. PCT/US2013/73958, filedDec. 9, 2013, which claims priority from U.S. Provisional Patentapplication No. 61/734,824, filed Dec. 7, 2012. The disclosures of theseapplications are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention relates in general to vehicle speed control devices thatregulate a user-selected vehicle speed level and, in particular, tospeed control devices having an off-road speed maintaining capability.

SUMMARY OF THE INVENTION

This invention relates to a vehicle speed control system, that in oneembodiment is configured with off-road performance features, that willallow the driver to travel at a set speed in a smooth, controlled manneron various unmaintained surfaces without requiring the driver to pressthe brake or accelerator pedal.

The invention concerns a vehicle speed control system for maintainingvehicle speed at a base target speed when the control system isactivated by a vehicle driver, the system comprising:

a slope sensor for directly or indirectly determining the slope of theground on which the vehicle is traveling;

a speed sensor for directly or indirectly determining the vehicle speed;

an engine controller for generating an engine torque request signal tooperate an engine/drivetrain so as to control the vehicle speed at anengine target speed;

a brake controller for generating a brake request signal to operatevehicle brakes so as to control the vehicle speed at a brake targetspeed;

wherein when the vehicle is traveling uphill the brake target speed isgreater that the engine target speed and the base target speedcorresponds to the engine target speed; and

wherein the engine and brake controllers cooperate to maintain thevehicle speed at or near the base target speed.

Preferably, when the vehicle is traveling downhill the brake targetspeed is less than the engine target speed and the base target speedcorresponds to the brake target speed. And, when the vehicle is at ornear a level condition, the base target speed corresponds to the braketarget speed. Optionally, the offset between the brake target speed andthe engine target speed when the vehicle is traveling uphill increaseswith increasing steepness. As a further option, the engine controllermay assume a passive operating state when the downhill slope exceeds apredetermined grade. The base target speed is selected by the vehicledriver.

As a separate and independent operating feature, the base target speedis a function of the slope on which the vehicle is traveling. As anotherseparate and independent operating feature, the base target speed is afunction of the steering angle.

Another separate and independent operating feature concerns that whenthe vehicle encounters an obstacle and the vehicle speed falls to ornear zero, the system operates to increase engine torque so as to climbthe obstacle; and wherein, at or near the time when the vehicle thenbegins to move (and the vehicle speed is still below the target speed),the vehicle braking is increased to preload the brake system prior tothe vehicle speed reaching the target speed.

Another separate and independent operating feature concerns that whenthe vehicle it traveling uphill and the driver requests braking, theengine controller continues to generate the engine torque request signaluntil the driver's braking pressure reaches a predetermined level whichis a function the steepness of the slope.

Another separate and independent operating feature includes a driveroperable terrain switch for selecting an operating mode generallycorresponding to a ground surface to be traversed (e.g., auto, rock,sand, mud, etc.); and wherein the engine controller operates at anadjustable engine gain for generating an engine torque request signal tooperate an engine/drivetrain so as to control the vehicle speed at thetarget speed; wherein the brake controller operates at an adjustablebraking gain for generating a brake request signal to operate vehiclebrakes so as to control the vehicle speed at the target speed; andwherein at least one of the engine gain and braking gain is adjusted asa function of the terrain switch.

Another separate and independent operating feature concerns that whenthe vehicle speed is below the base target speed, the engine controlleris operative to generate the engine torque request signal so as toincrease engine torque to increase the vehicle speed to the base targetspeed; and wherein when the vehicle encounters an obstacle and thevehicle speed falls to or near zero, the system operates in a hightorque mode for a certain time and then operates in reduced torque modeto at least temporarily reduce the engine torque.

Various aspects of this invention will become apparent to those skilledin the art from the following detailed description of the preferredembodiment, when read in light of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a 4WD vehicular configuration which may used toimplement the Select Speed Control features of the invention.

FIG. 2 is CAN interface architecture diagram for Select Speed Controlsystem.

FIG. 3 is a mode input/output diagram of the Select Speed Controlsystem.

FIG. 4 illustrates the control strategy at a constant base target speed.

FIG. 5 shows various SSC engine controller summary graphs.

FIG. 6A is a graph of target speed as a function of slope.

FIG. 6B is a graph of target speed as a function of steering angle.

FIG. 6C is a graph of target speed offset between the SSC-B and SSC-Econtrollers.

FIG. 7 is a flowchart of the speed target, SSC-B, and SSC-E operation.

FIG. 8 is a flowchart of Select Speed Control Maximum Gear Logic.

FIG. 9 is a flowchart of Select Speed Control Rear Differential CouplingRequest Logic.

FIG. 10A illustrates various stages of a vehicle traversing an obstacle.

FIG. 10B is a comparative plot of a brake pressure, open-loop request.

FIG. 10C are comparative plots of brake torque, engine torque, andvehicle speed for the obstacle traversing stages of FIG. 10A inaccordance with the invention.

FIG. 11A is a schematic illustration of a vehicle on a surface having aslope of Θ.

FIG. 11B is a plot of brake pressure versus surface slope θ.

FIG. 11C are comparative plots of brake torque, engine torque, andvehicle speed for the vehicle of FIG. 11A in accordance with theinvention.

FIG. 12A is a schematic illustration of a terrain selection switch.

FIG. 12B are comparative plots of brake torque, engine torque, andvehicle speed for various settings and operating conditions inaccordance with the terrain selector switch of FIG. 12A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

To facilitate this description, the following acronyms and definitionsmay be used:

Acronym/Term Full Form/Definition CAN Controlled Area Network CBCCentral Body Control Module ELSD Electronic-Limited Slip DifferentialEBCM Electronic Brake Control Module HDC Hill Descent Control HMI HumanMachine Interface PCM Powertrain Control Module TCM Transmission ControlModule SSC Select-Speed Control SSC-B Select-Speed Control BrakeController SSC-E Select-Speed Control Engine Controller

In one embodiment, the vehicle cruise control system is a Select SpeedControl Function (SSC) configured for use in on- and off-roadconditions. When fully activated, the SSC is adapted to maintain speedof the vehicle at a speed selected by the vehicle driver. While at leasta portion of the operating principles of SSC described herein areadvantageously used for low speed control applications, such as speedsup to about 10 KPH, at least some of the operating principles describedherein may be adapted for use in higher speed applications such as thosefound in, e.g., autonomous cruise control (ACC) systems. Preferably, theSSC system is adapted for use in a vehicle 10 of the type shown inFIG. 1. In particular, the vehicle may be equipped with the followinghardware components:

-   -   an engine 12    -   a transmission 14    -   a four wheel drive (4WD) system, or transfer case 16, with a        high numerical drive ratio, conventionally termed “4-Low”    -   a front differential 18 connected to front brakes 20 a, 20 b and        front wheels 22 a, 22 b    -   a rear differential 24 (which is typically an electronic locking        differential or “E-Locker”) connected to rear brakes 26 a, 26 b        and rear wheels 28 a, 28 b    -   a brake system including a brake pedal 30 operable by the        vehicle driver to selectively actuate the vehicle brakes    -   an electronically controlled vehicle stability/traction        control/anti-lock brake unit 32 interposed between the brake        pedal and the vehicle brakes 20 a,b and 26 a,b.

FIG. 1 also shows a series of control modules including an ElectronicBrake Control Module (with the Select Speed Control) 34, a PowertrainControl Module (PCM) 36, a Transmission Control Module (TCM) 38, aDifferential Torque Control Module (DTCM) 40, and a Central BodyController (CBC) 42. As represented by a block 44, each of these modulesis adapted to receive various sensor inputs from the vehicle, andgenerate selected control outputs to various electronically controlledcomponents. The various modules are further adapted to communicate withone via a CAN bus 46. The Powertrain (or Engine) Control Module (PCM) 36is preferably configured to perform one or more of the followingfunctions:

-   -   honor the torque request from the EBCM 34 for an indefinite        amount of time    -   populate instantaneous engine torque on a controlled area        network (CAN) bus 46    -   populate the driver requested torque signal on the CAN bus that        outputs idle control torque request during idle control    -   receiving and discerning actual accelerator pedal position

The EBCM 34, which includes Electronic Stability Control functionality,receives one or more of the following sensor inputs (sensors and inputsrepresented in part by block 44):

-   -   wheel speed sensors (single or bi-directional)    -   an accelerometer    -   a steering angle sensor    -   master cylinder pressure sensor

The TCM 38 provides the following functionality for the automatictransmission 14:

-   -   Functionality to upper limit the maximum gear of the        transmission with EBCM request capability in a system-enabled        (SSC_ENABLED) state    -   Functionality to lower limit the minimum gear of the        transmission with EBCM request capability in the SSC_ENABLED        State    -   ERS functionality supported by the transmission

The CBC 42 operates to provide the following functionality:

-   -   human-machine interface (HMI) for selecting target speed    -   HMI for displaying selected speed target    -   Lamp on the instrument panel for notifying the status of the SSC        system based the SelSpdLamp message output by the EBCM module    -   3-Level Compliant Driver Door Status message available on CAN        Bus    -   Parking Brake with CAN communication of status

Referring to FIG. 2, there is illustrated a CAN interface architecturediagram for the SSC system depicting the flow of communication betweenvarious modules and the CAN messages supported by the system. As shown,the electronic brake control module (EBCM) may control/communicate withthe vehicle powertrain (PCM), transmission (TCM), drivetrain (DTCM), andthe central body control (CBC) during Select Speed Control unless thedriver overrides through the use of the brakes, throttle, or disablingof the system.

The EBCM, which is the driver of the SSC function, may output CANmessages, shown in Table 1 below, to various modules to modulate theengine torque, transmission gear, lamp handling, and the coupling of therear differential to control the vehicle to the driver set target speedin a smooth manner while optimizing vehicle performance based on thedriver selected terrain.

TABLE 1 EBCM CAN Output Definitions for Select Speed Control Signal NameUnits Receiver Definition SelSpdSts Boolean CBC, Status of the selectspeed system. TCM “1” defines the system as “ON” and available to thedriver to modulate engine torque “0” defines the system as “OFF” andunavailable to the driver SelSpdLmp State CBC The command to illuminatethe Select-Speed Lamp on the instrument cluster and the Select-SpeedSwitch “00” Defines the system as “OFF” and both the instrument clusterlamp and the SSC Switch will not be illuminated “01” Defines the systemas “ON” and both the instrument cluster lamp and the SSC Switch will beilluminated continuously “10” Defines the system in an unavailable statedue to entry conditions or operating conditions are not satisfied andthe system will transition or remain in the “OFF” state, the lamp willblink during this command “11” Defined by the feature not beingsupported, SNA EngTrq_ Nm PCM The signal is defined as the torquerequest from the Rq_ESC EBCM module during the SSC “ON” state. This issignal is also utilized by other torque functions from the EBCM modulesuch as TC, YSC, EDTR, and MSR. The signal will be defined as the SSC-Erequested torque when the SSC is in the “ON” state to keep the vehicletraveling at the driver set target speed. When SSC-E is NOT activelyrequesting engine torque due to a driver throttle override or brakeoverride the signal will feedback the EngTrqStatic signal to the PCM.EngTrqMax_ Boolean PCM The signal is defined as TRUE when the EBCMRq_ESC module is requesting a torque increase from the PCM, and FALSEwhen the EBCM module is not requesting a torque increase from the PCM.In one embodiment, the signal is equal to “1” when the SSC-E torquerequest is greater than the EngTrqD_TTC signal * NOTE: In otherembodiments, the implementation may not be followed because theEngTrqD_TTC message will output the effective torque based on the EBCMmodule request. Therefore, the above- mentioned strategy for detectingdriver throttle override may not be supported by the specificarchitecture. Thus, the PCM module will supply a driver override signaland arbitrate control internally. This is the same strategy as ACC.Signal is equal to “0” when the SSC-E torque request is less than orequal to the EngTrqD_TTC signal. The engine is not to honor theEngTrq_Rq_ESC. GrMax_ Gear TCM The signal is defined as the upper gearlimit of the Rq_ESC transmission during SSC control “PASSIVE” is definedas NO upper gear limit request by the ESP module during a driveroverride event “G1” is defined as an upper gear limit of “1” during whenthe SSC feature is actively requesting engine torque in a forward drivengear “G2” is defined as an upper gear limit when the SSC-E is in the“OFF” state and SSC-B is “ON” during downhill control DES_R_ Nm DTCM Thesignal is defined as the rear differential coupling DIFF_TRQ requestfrom the EBCM module. During SSC control the rear differential isdesired to be coupled as a function of steering, inclination, andterrain select mode. The value should be calibrated to optimize off roadperformance.

The central body control module (CBC) may output the following CANmessages, shown in Table 2 below, to the EBCM for use in the SSCsubsystem.

TABLE 2 CBC CAN Output Definitions for Select Speed Control Signal NameUnits Receiver Definition VC_HDC_ Boolean EBCM “1” the vehicle isconfigured to have HDC Prsnt functionality. Only brake control isavailable “0” the HDC function is not supported on the vehicle VC_SSC_Boolean EBCM “1” the vehicle is configured to be an SSC vehicle Prsnt(SSC-B and SSC-E control are available to the driver) “0” the SSCfeature is not supported in the vehicle HILL_ Boolean EBCM “1” thedriver is pressing the HDC/SSC button to DES_RQ enable or disable thesystem “0” the driver is not currently pressing the HDS/ SSC button DRV_Boolean EBCM “1” the driver door is ajar AJAR “0” the driver door isclosed PARK_ Boolean EBCM “1” the park brake is engaged BRK_EGD “0” thepark brake is not engaged

The powertrain control module (PCM) may communicate the following CANmessages, shown in Table 3 below, to the EBCM to assist in the operationof the SSC function.

TABLE 3 PCM CAN Output Definitions for Select Speed Control Signal NameUnits Receiver Definition EngTrqD_TTC Nm EBCM The signal outputs thedriver demanded propulsion torque EngTrqStatic Nm EBCM The signaloutputs the instantaneous torque output by the engine AccelPd1Posn %EBCM The signal outputs the virtual position of the pedal equivalent tothe EngTrqD_TTC corresponding torque output. ActlAccelPedPosn % EBCM Thesignal outputs the physical (future) position of the accelerator pedalposition

The PCM interface may optionally include a driver override function todetermine when the driver is overriding the SSC torque request, that isinternal to the PCM, and may be configured to set the SSC engine torquerequest to the “PASSIVE” state within the EBCM. A driver override CANmessage may be sent out by the PCM when the driver is overriding the SSCtorque request, similar to the architecture of a conventional AdaptiveCruise Control (ACC). This configuration may provide a more robustimplementation of the driver override detection because the PCM isresponsible for the torque signals and the accelerator pedal position.Thus, internal detection of the necessary inputs would be more robustdue to internal fail safes on the signals. In addition, this embodimentmay further improve the HMI interface to the driver by displaying amessage that the driver is overriding the SSC system on the cluster. Inaddition, the EngTrqD_TTC signal will mirror the SSC-E torque requestwhen the SSC function is actively modulating the engine torque. Also,the AccelPdlPosn signal will calculate the virtual pedal based on theSSC torque request during SSC control.

The transmission control module (TCM) may output the following CANmessages to the EBCM for use in the operation of the SSC. During SSCcontrol, the transmission module may be configured as a slave to theEBCM in order to maintain the proper gearing to optimize the off roadperformance and smoothness of the SSC-E and SSC-B controller. As shownin Table 4 below, the transmission control module (TCM) may provide oneor more of the following outputs.

TABLE 4 TCM CAN Output Definitions for Select Speed Control Signal NameUnits Receiver Definition PRNDL_DISP Gear EBCM The signal outputs thePRNDL (Park, Reverse, Neutral, Drive, Position Low) position to thedriver on the instrument cluster. For SSC control, the ERS functionalitywill display the speed target (1-8, N, R) for SSC. Gr Gear EBCM Thesignal communicates the current gear of the transmission. Gr_Target GearEBCM The signal communicates the target gear of the transmission. Thedelta between Gr_Target and Gr define a shifting condition of thetransmission.

The TCM may optionally default to a SSC specific transmission shift mapwhen the SSC function is in the “ON” state. This configuration willallow the transmission to be calibrated specifically for SSC performanceto eliminate the harshness associated with the handover between SSC andTCM control of the transmission during driver throttle override events.In addition, the speed target being limited as a function of grade iscurrently executed internally to the EBCM without informing the driver.Thus, as the vehicle climbs a steep hill, the speed target may belimited although the driver perceives that the PRNDL_DISP is the vehicletarget speed. as a consequence, if the limited speed is slower than thedriver desires, the driver may increase the target speed. In thisembodiment, the EBCM may ignore the speed increase due to the internalgrade speed limitation. As the driver crests the hill, the internaltarget speed will approach the driver selected target speed as afunction of grade. This may result in the vehicle suddenly acceleratingdue to the change in target speed as a function of slope. As analternative in this embodiment, a clean interface for this functionalitymay allow the EBCM to limit the PRNDL_DISP value based on the internalgrade limitation and any other internal target speed limitations. APRND_MAX messages can be implemented to overwrite the PRNDL_DISP gear asthe target speed is limited by the EBCM. This will inform the driver ofthe internal modification of the target speed. Also, the PRNDL_DISP isnormally not increased by the EBCM once the limitation condition nolonger exists. In another variation of this embodiment, the driver mayincrease the target speed manually with paddles. This will improve thedriver interface, and eliminate sudden accelerations as the drivercrests a steep hill with a higher target speed than the internal gradelimited target speed.

The drivetrain control module (DTCM) may be configured to output thefollowing CAN messages, shown in Table 5 below, to the EBCM for use inthe operation of the SSC function.

TABLE 5 DTCM CAN Output Definitions for Select Speed Control Signal NameUnits Receiver Definition TCASE_ State EBCM The signal will output thestatus of STAT the transfer case and communicate whether the drive trainin the 4Low state for SSC to activate. *Note: This signal can bevalidated with an internal plausibility diagnostic. NetCfg_ Boolean EBCMThe signal will output whether the rear ELSD differential is present onthe vehicle and active. This is a robustness check because the SSCsystem may typically not function without a functional rear differentialon the vehicle.

In operation, the Select Speed Control (SSC) function may be defined tohave two states: ON and OFF. The states can be communicated to othervehicle modules through the use of the SelSpdSts message.

Under the CAN Protocol, when SelSpdSts=1, the SSC function is ON. TheSSC function is ON when the function has been enabled by the driver andthe Selec-Speed Brake Control Brake Controller (SSC-B) and Selec-SpeedControl Engine Controller (SSC-E) are readily available to control theirrespective outputs to maintain the driver selected target speed. To thedriver this state is represented by a continuously illuminated SSC lamp.It is noted that the SSC ON state does not need to contain any specificinformation on the status of individual SSC-E and SSC-B controllers. Itmay, however, be configured to convey that the SSC-B and SSC-E areavailable to the other modulates. In this embodiment, the SSC system maybe configured with the following SSC Function Enabling Criteria in theON state:

-   -   No EBCM faults are present        -   AND    -   The driveline is confirmed in the low range, which will be        confirmed by internal calculation when OEM verifies that the        sending module of CAN status message is not a robust signal.        -   AND    -   Driver is not applying the throttle        -   AND    -   Vehicle speed is below a entry threshold [8 kph]        -   AND    -   The PRNDL is confirmed in Park        -   OR    -   Vehicle is in Neutral, Drive, or Reverse        -   AND    -   Driver Door is not open        -   AND    -   Park Brake is not engaged        -   AND    -   HMI SSC Button is pressed

The SSC ON state may include a number sub-states, including SSCON-Active Brake, SSC ON-Active Engine and SSC On-Passive.

The status of the SSC-B controller is determined to be active when thecontroller is actively requesting brake pressure. The status of thebrake controller does not need to be directly conveyed via the CAN Busduring control with a unique message; however, the BrkTrq messageoutputs the estimated BrkTrq requested by the EBCM module. In thisembodiment, the SSC-B controller may be active under one or more(including all) of the following conditions:

-   -   SSC ON State present        -   AND    -   Indicated gear selection is any forward gear selection (D or        numeric value), Neutral, or Reverse        -   AND    -   Vehicle speed is below a tunable threshold (first trial 20 mph)        -   AND    -   Brake pressure is requested by SSC-B controller        -   AND    -   Driver is not braking greater than the SSC-B request

The status of the SSC-E controller is determined to be active when theSSC-E torque request (EngTrq_Rq_ESC) is greater than the driverrequested torque (EngTrqD_TTC). The SSC ON-Active Engine state ispresent when the EngTrqMax_Rq_ESC is “1”. In this embodiment, the SSC-Econtroller may be activate under one or more (including all) of thefollowing conditions:

-   -   SSC ON State is present        -   AND    -   Indicated gear selection is any forward gear selection (D or        numeric value), or Reverse        -   AND    -   SSC-E torque request is greater than Driver Requested Torque        (EngTrqD_TTC)        -   AND    -   Vehicle is on slope greater than tunable threshold (−15%)        -   AND    -   Driver braking input is below a threshold

The SSC system may have one or more (including all) portions set to apassive state, indicated as SSC ON-PASSIVE. In this state, the SSCfunction has been enabled by the driver, and neither, the SSC-B or theSSC-E is actively controlling the related subsystems. In thisembodiment, the SSC-E and SSC-B controllers may be set to a passivestate, while remaining available when one or more (including all) of thefollowing conditions are present:

-   -   SSC ON State is present        -   AND    -   Indicated gear selection is any forward gear selection (D or        numeric value), or Reverse        -   AND    -   SSC-E torque request is greater than Driver Requested Torque        (EngTrqD_TTC)        -   AND    -   Vehicle is on slope greater than tunable threshold (−15%)        -   AND    -   Driver braking input is below a threshold

The status or indicator lamp is configured to signal to a driver to acondition of the operative SSC state. The lamp may be configured toindicate the SSC-ON State as follows: In the SSC ON-PASSIVE state, whenthe vehicle is over a predetermined speed (e.g., 20 mph) the lamp willflash for a certain time period (e.g., a maximum of 70 seconds) and thenautomatically disable. In addition, during this flash condition when thedriver presses the HMI button or the vehicle speed exceeds a secondhiher predetermined speed (e.g., 40 mph), the lamp will cease to beilluminated and SSC will transition to the SSC-OFF State. Other lampsignaling architectures may also be used to indicate the SSC state, ifdesired. In a specific embodiment, shown below in Table 6, the lampsignaling conditions may operate under one or more (including all) ofthe conditions indicated:

TABLE 6 SSC-ON State Lamp Handling SSC ON State Conditions Lamp ActionSSC ON-ACTIVE BRAKE See above Solid Lamp SSC ON-ACTIVE ENGINE See aboveSolid Lamp SSC ON-PASSIVE due to Vehicle is shifted to P Solid Lampdriver brake or throttle OR override SSC-E torque request is less thandriver requested torque (add signal) AND SSC-B is passive SSC ON-PASSIVEOver Vehicle speed exceeds Flash Lamp for Speed Warning a tunablethreshold maximum of 70 (first trial 20 mph) seconds

Under the CAN Protocol, when SelSpdSts=0, the SSC function is OFF. TheSSC OFF state is defined as by the following conditions: the Selec-Speedfunction is not enabled, and the SSC-B and SSC-E controllers areinhibited from modulating their respective control outputs. To thedriver, this state is represented by a non-illuminated SSC lamp. The SSCOFF state can be present in the following scenarios:

-   -   the driver has not enabled the SSC function.    -   the driver presses the HMI button when the system is not current        enabled and not all the SSC entry conditions are satisfied. The        lamp may flash for a minimum of 2 seconds and a maximum of 5        seconds.

In addition, the transition from the SSC ON-ACTIVE to the SSC OFF statewill occur in a controlled manner with a flashing lamp for a minimum of2 seconds based on the following conditions:

-   -   The driveline is no longer confirmed in the low range        -   OR    -   The driver door is opened        -   OR    -   An EBCM fault is detected        -   OR    -   The park brake is engaged.

The SSC function can transition from the SSC ON-ACTIVE to the SSC OFFstate when the system is currently enabled and the HMI button is pressedwith no flashing of the lamp. The SSC function can transition from theSSC ON-PASSIVE to the SSC OFF state when one or more of the followingconditions are present:

-   -   The driver presses the HMI Button        -   OR    -   The vehicle speed is greater than 20 mph for 70 seconds        -   OR    -   The vehicle speed is greater than 40 mph

As shown below in Table 7, the lamp actions associated with SCC OFFstate transitions and conditions are presented.

TABLE 7 SSC-OFF State Lamp Handling SSC State Transition Conditions LampAction SSC OFF The system has not been No lamp enabled by driver SSC ON-> OFF The driver presses the SSC Solidly Illuminated Lamp Transition byDriver HMI button Request AND The driveline is confirmed in the lowrange AND The driver door is closed AND The vehicle speed is below 20mph AND No EBCM fault is present AND The park brake is not engaged SSCON-Passive-Over The driver presses the SSC No Lamp Immediately Speed ->OFF Transition HMI button by Driver Request AND The vehicle speed isabove 20 mph SSC ON-Passive-Over The vehicle speed is above No LampImmediately Speed -> OFF Transition 20 mph for 70 seconds by Max OverSpeed Timer SSC ON-Passive-Over The vehicle speed is above No LampImmediately Speed -> OFF Transition 40 mph by Maximum Speed SSC ON ->OFF The driveline is no longer 5 Second Lamp Flash Transition by Invalidconfirmed in the low range **Note: If the conditions Condition ORcausing the transition to the The driver opens the driver OFF aresatisfied during the door flash, the flash should timeout OR with aminimum time of 1 An EBCM fault is detected second OR **Note: If driverpresses the The park brake is engaged button during the flash, the ORflash is immediately cancelled Thermal Fault SSC OFF -> OFF HMI buttonis pressed 5 Second Lamp Flash Transition by Invalid AND **Note: If theconditions Condition The driveline is no longer causing the transitionto the confirmed in the low range OFF are satisfied during the OR flash,the flash should timeout The driver opens the driver with a minimum timeof 1 door second OR **Note: If driver presses the An EBCM fault isdetected button during the flash, the OR flash is immediately cancelledThe park brake is engaged

Referring to FIG. 3, the moding of the SSC function is graphicallydepicted.

If a Hill Descent Control (HDC) feature is contained within the EBCM,the SSC system can be considered an extension of the HDC. Typically, theHDC system is designed to work on downhill slopes greater than athreshold, and it automatically modulates the brake pressure to controlthe vehicle speed to a driver set target speed while descending a hill.Gravity and idle torque, when the driveline is engaged, are the forcespropelling the vehicle downhill. The HDC brake controller is referred toas SSC-B in the context of the Select Speed Control subsystem. The SSCsystem is composed of two concurrently running controllers that willmodulate brake pressure and engine torque separately to maintain thedriver selected target speed. The Select Speed Control engine controlleris herein referred to as SSC-E. The SSC-E controller may be contained inthe EBCM, and request the necessary torque for the vehicle to maintainthe driver selected target speed in a slow, controlled manner when thevehicle is on a slope greater than a threshold. The control strategy ata constant base target speed is illustrated in FIG. 4.

In addition to control of the brake and engine torque, the SSC functioncan use the gear selector (PRNDL) display to determine the driver settarget speed with various internal modifications, control the maximumgear of the transmission, and the coupling status of the E-Locker whenSSC is in the “ON” state.

The SSC-B controller can be configured to provide an HDC function thatmodulates the brake pressure to maintain the driver selected targetspeed as the vehicle travels down a slope steeper than a threshold. Whenthe controller is configured as part of the SSC subsystem, theconditions may be modified to allow the SSC-B controller to modulate thebrake pressure on all slopes. Thus, the SSC-B controller may be readilyavailable once the driver has enabled the function through the HMI,independent of grade. The controller allows the driver to overlay abrake request and seamlessly take control of vehicle braking. Inaddition, any throttle override input by the driver will result in aramp out of the brake pressure. In order to optimize performance of theSSC function, the SSC-B controller can use the information from aTerrain Select dial to modify control and/or calibrations for the driverselected surface. Any alternative or specific Hill Descent Controlalgorithm may be the foundation for the SSC-B.

Optionally, an SSC Rock Mode Brake Controller may be provided to addressspecific driving conditions or terrain. When a driver selects the RockMode, it may be assumed that the driver is on a surface such as a rockgarden, or boulders. In order to minimize overshoots of the SSC control,an open loop term is added to the SSC-B controller to emulate two footdriving.

The SSC-E controller modulates the torque request to the engine controlmodule. The activation of the SSC-E controller may be inhibited when thevehicle is traveling down a slope steeper than a threshold (e.g., 15%).On a slope steeper than the threshold, SSC-E is set to the passive statebecause gravity and idle torque forces are sufficient for the vehicle tomaintain the target speed. Under these conditions, the vehicle functionsonly with the SSC-B controller. The SSC-E controller is a PI controllerwith an open loop term. The input to the SSC-E controller is the errorbetween the target speed and the vehicle speed. The equation for thecontroller is:Y=[Ki∫^(□) ^(□) e(t)dt+I_Hill(grade)]+Kpe(t)Where,

-   -   Ki∫^(□) ^(□) e(t)dt: speed error integrated over time multiplied        by a gain factor (Ki)    -   I_Hill: is equivalent to the torque required to hold the vehicle        stationary on the estimated slope    -   Kpe(t): the proportional control error multiplied by a gain        factor (Kp)        The open loop term referred to as the I_Hill term is defined as        the minimum engine torque necessary to hold the vehicle        stationary on the slope with no brake pressure in the system. In        this embodiment, the I term is the dominant term in the        controller for the vehicle to maintain the driver selected        target speed, and is subject to gain scheduling based on the        vehicle speed target. In addition, the SSC-E control output        should initialize to the feedback torque by pre-loading the I        term when the SSC-E activation conditions are met. A graphical        summary of the SSC-E control is shown in FIG. 4.

The SSC-E controller is defined as being active when the SSC-E torquerequest is greater than the driver requested torque, the drive is notbraking above a threshold, and the driveline is in a forward driven gearor reverse. This activation condition allows seamless driver torqueoverlay as the SSC-E controller transitions from the active to passivestate. These transitions require the pre-loading of the I-term tomaintain smooth control following a driver throttle or brake override ofthe system. To optimize the performance of the SSC function, it may bebeneficial to permit the ability to gain the controller for each of thesurfaces available on the Terrain Select dial.

Timeout logic of the SSC-E torque request may be implemented in order toprotect the driveline from harm due to high torque requests by the SSC-Econtroller. Once an undesired situation due to the SSC-E torque requestis determined, the SSC-E controller must reset to the torque requestequivalent to the I Hill torque for 3 seconds; then the controller mayreinitialize to the active state. The reset mechanism to the I Hilltorque is beneficial because the limits can be reached on steep slopesand resetting to idle torque (the SSC-E Passive State) will result insignificant roll back of the vehicle. The undesired torque requests aredetermine by the following checks:

-   -   The SSC-E can only request torque above a maximum torque (e.g.,        240 Nm) threshold for a predetermined time (e.g., 2.5 seconds)        when the vehicle is stationary.    -   The SSC-E can only request torque above a maximum torque (e.g.,        240 Nm) threshold for a predetermined time (e.g., 3 seconds)        when the vehicle is moving.    -   The Traction Control system brake limited differential brake        request has reached the maximum request for a predetermined time        (e.g., 1.5 seconds).    -   The rear axle is coupled and in a slip condition above a        threshold rate for a predetermined time (e.g., 0.75 seconds).        The addition of more torque will only increase the slip        condition resulting in harm to the driver or driveline; if the        tires were to gain traction at the high torque level (commonly        seen on sand and loose dirt surface)

The driver selected target speed is the base target speed that the SSC-Eand SSC-B controllers control to; however, there are several influencesthat can modify the SSC-E and SSC-B target speed. Referring to Table 8below, and FIG. 6A, the target speed influences are:

-   -   PRNDL display on EVIC—the selected PRNDL position will determine        the base target speed (See Table 8)    -   Slope—the control target speed is upper limited on high slopes        independent of the driver selected target speed (see Table 8)

TABLE 8 Select Speed Control Target Speed as Function of PRNDL and GradeTarget Speed in Target Speed in Gear KPH for grade <15% KPH for 100%grade P n/a n/a R 1 1 N 2 (HDC functionality only) 1 D If D is supportedand D is selected 1 during SSC entry target is 1 kph. If SSC is enabledbefore shifting to D, the speed target for D will be carried over tomatch the previously selected target. 1 1 1 2 2 1 3 3 1 4 4 1 5 5 1 6 61 7 7 1 8 8 1 9 9 1

In another embodiment, a steering wheel angle is measured and inputtedinto the system. To prevent binding of the rear axle and crow hop, ahigh input of steering on a slope within an upper and lower limit willdecrease the controller target speed to a maximum target speed. If theslope is outside the limits, no steering angle adjustment is performedon the base target speed. The input is the absolute value of thesteering angle. Table 9 shows an embodiment of target speed limits as afunction of steering angle and slope.

TABLE 9 Select-Speed Control Target Speed Limits as a Function ofSteering Angle and Slope Steering Angle Upper Speed Target LimitAdjustment Band 300 8 (Maximum Gear) −15%< slope <15% 600 2 −15%< slope<15%

It will be appreciated that the specific relationship between the driverselected target speed, slope and steering angle can vary depending onthe specific vehicle operating characteristics.

In addition to the internal adjustments on the control speed target, thetarget speed of the SSC-E and SSC-B controllers are offset, as shown inFIG. 6C, to prevent wind-up of the two controllers. The SSC-E and SSC-Bcontrollers are preferably prioritized as a function of downhill anduphill traveling conditions. Preferably, it can be advantageous tosimultaneously operate both the engine and brake controllers over atleast portion of the terrain being traversed. This is particularlydesirable when the vehicle is traveling uphill, or when the vehicle isin certain operating modes such as on a ROCK terrain. However, duringthese portions of the control it is desirable to introduce an offsetbetween the engine target speed and the brake target speed so as toprevent system windup of the two simultaneously operating controllers.When traveling uphill, it is preferable for the brake target speed to begreater than the engine target speed, and for the engine target speed tocorrespond to the base target speed. When traveling downhill, or whenthe vehicle is at or near level, it is preferable for the engine targetspeed to be greater than the brake target speed, and for the braketarget speed to correspond to the base target speed. As shown in FIG.6C, when traveling uphill the offset may increase with increasing slope.And, while the downhill offset is shown as being generally constant overthe entire downhill range, in some instance it may be desirable toinhibit the SCS-E controller at a predetermined downward slope −x (e.g.,−15%), such that its output corresponds to idle torque.

Referring to FIG. 7, there is shown a flowchart representing theoperation of the SSC-B and SSC-E controllers.

In one embodiment, the SSC function may be configured to request themaximum gear that the transmission can maintain during SSC ON control.The transmission may be configured to honor the request when the SSCfunction is enabled. Table 10, below, describes the implementation ofthe SSC gear request when the SSC function is enabled.

TABLE 10 Maximum Gear Logic for Select Speed Control Gear Max. CaseRequest SSC not enabled PASSIVE SSC Enabled PASSIVE Vehicle not inforward driven gear Engine control only 1 Slope less than SSC-Eactivation threshold 2 Driver throttle override PASSIVE SSC-E PassiveFollowing driver throttle override vehicle PASSIVE above speed thresholdFollowing driver throttle override vehicle 1 below speed thresholdcalibrate for smooth handover from transmission control to SSC gearcontrol

In a variation of this embodiment, the SSC performance may be configuredas a Transmission Shift Map with shifting biased toward higher RPMvalues to be used during SSC-control. This may eliminate any harshhandover of control of target gear position between the transmission andthe EBCM following a driver throttle override event. Referring to FIG.8, there is shown a flowchart of the maximum gear logic.

The E-Locker differential configured for implementation of SSC is anelectronic limited slip differential. When SSC is in the “ON” state, acoupling request is sent to the ELSD as a function of the absolute valueof the steering angle when the estimated slope of the surface is below athreshold predetermined threshold indicative of a relatively flatterrain such as, e.g., +/−15%. If the estimated slope is above thisthreshold, the ELSD is requested to couple with the maximum force(100%). This slope threshold is implemented to prevent crow hop andbinding on flat ground with a large steering input. Table 11 below showsexamples of the relationship between steering angle, coupling requestand the slope.

TABLE 11 ELSD Control Look Up Table Steering Angle Coupling Request in %Slope 300 degrees 100 −15%< slope <15% 500 degrees 80 −15%< slope <15%620 degrees 30 −15%< slope <15%

In a variation of this embodiment, the coupling request may only beallowed when the conditions are satisfied for SSC-E to enter the activestate. The coupling request can also be tunable when the Select TerrainDial is in the Rock position. This is done to maximize the performanceof the vehicle by forcing the vehicle to remain a true 4-wheel-drivevehicle. Referring to FIG. 9, there is shown a flowchart of the logicassociated with the rear differential coupling request.

Another variation of this embodiment configured for the interface withthe rear differential, is to allow the rear differential to arbitratebetween the EBCM coupling request and their desired coupling request.The current implementation makes the rear differential a slave to theEBCM; thus, the coupling is only performed by request. The reardifferential, which has history with off road performance, can belimited to honor the EBCM request only when it is greater than theirinternal request.

Another feature of the SCS control is shown in FIGS. 10A-10C. FIG. 10Ashows the vehicle traversing an obstacle 60 in stages A, B and C. FIG.10B shows an brake open loop request 62 as a function of slope. FIG. 10Cshows in solid lines the vehicle speed, engine torque and brake torquewhen using this feature of the invention, while the respective behaviorwithout the invention is shown by dashed lines.

In FIG. 10A at stage A, the vehicle is traveling along a generally levelsurface and has encountered the obstacle 60. The obstacle causes thevehicle speed to drop to or near zero at time t0, as shown in FIG. 10C.At this point the engine torque is increased at 64 to cause the vehicleto being to move at time t1. According to one feature of the invention,at or near the time the vehicle being to move (time t1), the open loopbrake request 62 is introduced at 66. As a result of the brake request66, the vehicle speed is controlled so that any overshoot of vehicle attime t2 speed is reduced at 68. Without the brake torque increase attime t1, the brake response would be delayed, as shown at 70, such thatthe vehicle speed overshoot would be significantly higher, as shown at72.

Another feature of the SSC control is illustrated by FIGS. 11A-11C. InFIG. 11A, the vehicle is shown as traveling upward on a hill with aslope of Θ, and acted on by a downward gravity force=mg (sin Θ). As longas the SSC remains active, the engine torque will be controlled toovercome this downward force, and maintain the vehicle speed as selectedby the driver. In the event the driver steps on the brake, the enginetorque request will be reduced as the brakes are applied. FIG. 11B showsthe brake pressure necessary to hold the vehicle on a hill as a functionof the slope Θ. Normally, on level ground and up to a slope of x0(generally about 30%), and during a normal brake application of y0(generally about 5-10 bar), the engine torque signal generated at idleis sufficient to prevent vehicle rollback. However, on slopes greaterthan x0, it may take increased brake pressure, as represented by theramp 80. For example, at slope x1, a brake pressure of y1 is required toprevent vehicle rollback. Thus, in the event the driver depresses thebrake pedal when the vehicle is traveling uphill, it is important thatthe engine torque request is not inhibited or reduced so quickly so asto cause the vehicle to roll back. The control feature illustrated inFIG. 11C ensures that sufficient brake pressure is generated in a steepuphill condition before the system allows the existing engine torque tobe reduce to idle, by requiring the brake pressure reach a certain levelbefore the engine torque is reduced.

FIG. 11C shows the vehicle speed, engine torque and brake torque as thedriver applies the brake when SSC is active and the vehicle travels anuphill slope of x1. The solid lines represent the respective values whenthe enhanced control feature of the invention is used, while the dashedlines show the system response without this enhanced control feature. Asshown in FIG. 11C, at time t0, the driver begins to press the brakepedal. Initially the engine torque remains applied. Then at time t1brake pressure reaches y0, which is the minimum threshold pressurerequired to inhibit engine torque, as long as the measured slope is lessthan x0. According to this control feature, when the slope is greaterthan x0, the engine torque is not reduced at time t1, but remainsapplied or even slightly increased, as shown at 82. During this time thevehicle slows, as shown at 62. The engine torque remains elevated untiltime t2, which corresponds to the point when the driver applied braketorque reaches y2, which is the system pressure required to hold thevehicle stationary on the slope x2, with engine torque at idle. At timet2, engine torque is quickly reduced to idle torque, wherein the vehiclecomes to a stop. Without this modified control strategy, the enginetorque would normally be reduced beginning at time t1, and would reachidle torque before time t2. In this case, at 84, the vehicle would beginto roll backward for a short time period, before it would then come to astop.

Another feature of the SSC system is illustrated in FIGS. 12A and 12B.According to this feature the gains of the SCS-B controller and theSCS-E controller are adjusted as a function of the position of theterrain select switch 88 shown in FIG. 12A. Generally when the switch isin the AUTO or SNOW positions the respective gains will be relativelymoderate. However, when in ROCK mode, it can be advantageously toincrease the gain of the engine controller, while reducing the gain ofthe brake controller. When in the SAND or MUD position, it isadvantageous to increase the gain of the brake controller, and todecrease the gain of the engine controller.

As shown in FIG. 12B, depending on the particular terrain the vehicle istraveling, it is desirable to adjust the gain of controller toaccommodate varying terrains. This is particularly important for theengine controller. For example, in a rocky terrain, a lower gain enginecontrol is preferred (at 90), while in sand or mud conditions, a highergain engine controller is preferred (at 92). For “auto” type settings,the engine controller gain can be set at a medium level (at 94). Withrespect to the brake controller, it is preferred that in a rocky terraina high brake gain is selected (at 96). In sand or mud, a lower brakegain is preferred (at 98). For “auto” type settings, the brakecontroller gain can be set at a medium level (at 100).

In summary, the Select-Speed Control function optimizes off-road vehicleperformance by modulating the engine and brakes autonomously whileallowing the driver to concentrate on the path of vehicle with onlysteering as an input. The system provides the capability to ascend ordescend any obstacle that a typical driver could navigate within thelimits of the vehicle.

The principle and mode of operation of this invention have beenexplained and illustrated in its preferred embodiment. However, it mustbe understood that this invention may be practiced otherwise than asspecifically explained and illustrated without departing from its spiritor scope. Additionally, each embodiment disclosed herein may be a standalone component or combined with any or all of the other embodimentsdisclosed herein.

What is claimed is:
 1. A vehicle speed control system for maintainingvehicle speed at a target speed when the control system is activated bya vehicle driver, the system comprising: a speed sensor for directly orindirectly determining the vehicle speed; an engine controller forgenerating an engine torque request signal to operate an engine;drivetrain so as to control the vehicle speed at the target speed; brakecontroller for generating a brake request signal to operate vehiclebrakes so as to control the vehicle speed at the target speed; wherein,when the vehicle encounters an obstacle and the vehicle speed falls toor near zero, the system operates to increase engine torque so as toclimb the obstacle; and wherein, at or near the time when the vehiclethen begins to move and the vehicle speed is still below the targetspeed, the vehicle braking is increased to preload the brake system as afunction of the target speed by preloading the brake system prior to thevehicle speed reaching the target speed.